New Passivity Observers for Improved Robot Force Control

Abstract

Abstract— This paper extends the previously proposed Explicit Force Controller based on Time Domain Passivity Approach. When using the classical passivity observer, we encounter an energy accumulation problem : if the system stays a long time in stable contact, energy is dissipated and the passivity observer builds up a large value. This cause the passivity controller to be triggered very late when the interaction becomes unstable, and we lose the advantage of the passivity controller. In order to deal with this energy accumulation issue, we propose two new passivity observers that ”forget” about energy previously dissipated. We prove the theoretical validity of these new observers. In addition, we propose a more generalized way of implementing the passivity based explicit force controller on a multi DoF manipulator, using a model for the robot and environment that includes sensor flexibility, and a Hybrid Position/Force controller in the operational space framework. The proposed method is experimentally tested with KUKA LWR, and the improved performance is verified.